Process for stabilization of copper treated oils



Patented May 20, 1941 PROCESS FOR STABILIZATION OF COPPER TREATED OILSWalter A. Schulze, Bartlesville, Okla., and Graham H. 'Short, Phillips,Tex., assignors to Phillips Petroleum Company, a corporation of DelawareNo Drawing. Original application November 9,

1938, Serial No. 239,731. Divided and this application May '28, 1940,SeriahNo. 337,733

2 Claims;

This invention relates to a new and useful process for treatinghydrocarbon oil. More specifically, this invention relates to a processfor stabilizing or preventing the deterioration of hydrocarbon oil whichhas undergone a purifying 5 copper reagents whereby the sweetened. oilistreatment with reagents containing copper. stabilized againstdeterioration by. the removal This application is a division of ourcopending therefrom of retained copper salts. application Serial No.239,731, filed November 9, Another object of this invention'is the con1938. version of oil-soluble copper compounds present Hydrocarbon oil,particularly petroleum 'disin hydrocarbon oil as a result of sweeteningwith tillates usually contain impurities, including sulcopper reagentsto oil-insoluble compounds, said fur compounds, which cause the oil toexhibit conversion resulting in complete separation of undesirableproperties such as bad odor and gum the insoluble copper compounds fromthe oil. and color formation. It is customary, therefore, Schulze andFrey in U. S. Patent No. 1,980,555 to subject said impure oil to apurifying treatdescribed a method for stabilizing an oil treated ment inorder to remove theimpurities or to with copper and which exhibiteddiscoloring convert them to less objectionable forms, for and/orformation of resinous matter, polymers example, the conversion ofmercaptans tmdisuland oxidation products; that is, a method of fides.stabilizing the oil by bringing it in contact with The methods oftreatment for the removal or an alkaline sulphide solution subsequent totreatconversion of mercaptans make use of various ing with the copperreagent. I chemical processes, and of these processea'one We have nowdiscovered that copper treated of themost satisfactory is the processutilizing oils may be stabilized by means other than the copper, saltsof copper, or solutions-containing alkaline sulfide solution referredtoabove and copper salts. that these means involve certain improvementsHowever, subsequent to treatment with copand advantages, This discoveryis extremely per-containing reagents, it has been found that importantin that it clearly defines the condimany hydrocarbon oils requirefurther treatment tions which must be met to produce stabilized orstabilization. This condition is due to the oils. This'discovery,likewise makes it possible fact that said unstable oils retain from.their to divide treating agents into two groups, the contact with copperreagents, extremely small first group consisting of those reagents whichquantities of oil-soluble copper compounds. will effectively remove thehydrocarbon oil-solu- These traces of copper compounds remaining in blecopper compounds and thereby stabilize the the oil are responsible forthe marked accelera- Q oil, and the second group consisting of. thosetion of reactions which lead to the formation in reagents which will notremove suflicient quansaid oil of color, gum, resinous deposits andpolytitles of the copper compounds to stabilize the mers; thesedeteriorative changes seriously imoil. pair such properties of the oilas color, gum con- We have found that copper mercaptides intent andoctane number. crease in solubility in the oil with increasingOne-object of this invention is to effect the 40 molecular weight ofthemercaptans. Copper removal of traces of copper compounds from hymethylmercaptide is the most insoluble of all drocarbon oils. the coppermercaptides and is almost totally Another object of this invention isto-preve'nt insoluble inhydrocarbon oils. -.Copper ethyl merthedeterioration of hydrocarbon oil which has captide, the next number inthe series, is a litbeen re wi h c pp r re ents by the removal 'tle moresoluble, yet its actual solubility figure is from said oil of smallamounts of retained oilsoluble copper compounds responsible foraforesaid deterioration.

pounds subsequent to sweetening with copper reagents, to remove saidcopper from the oil,

thereby delaying or preventing deterioration.

Another object of this invention is to provide a step in the sweeteningof hydrocarbon oil with extremely low. Copper butyl mercaptides and amylmercaptides-are .much more soluble'and their solubilities may bedetermined in the usual manner of precise measurements.

We have now discovered that hydrocarbon oil 'containing copper methylmercaptide, and thereforecompletely saturated with respect to thesubstance, does not show any of the undesirable reactions'mentionedabove as resulting from the catalytic effect of dissolved coppercompounds.

' 'tion of copper methyl mercaptide in hydrocarbon oil is too low tocause deterioration of the oils. On the other hand, we have found thatif the hydrocarbon is saturated with respect to copper ethyl mercaptide,the concentration of copper is just sufiicient to cause a slowdepreciation in the said properties of the oil. Thus, we

have established that there is a critical value for copper concentrationin the oil, above which deterioration will occur, and below which theoil will be stable as regards gum and color formation in storage.

This improved process of stabilization depends on the efiective removalof traces of copper compounds from the contaminated hydrocarbon oil bytreating said oil to completely convert the hydrocarbon oil-solublecopper compounds into compounds whose solubility is less than thesolubility of the copper salt of ethyl mercaptan. By this means, andthesubsequent separation of these more insoluble compounds from thehydrocarbon oil, the deterioration due to dissolved copper compounds inthe oil is prevented.

Since the deterioration of oil is accelerated in a catalytic manner bydissolved copper salts, it follows that copper salts more insoluble thancopper ethyl mercaptide are inactive as catalysts for deteriorativereactions in oil, and likeof the copper is not effected by treatment ofthe oil with caustic soda, carbonate or phosphate solutions, or by theaddition to the oil of controlled amounts of ethyl mercaptan,

In order to explain more exactly the criterion by which thestabilization of copper-containing oil is judged, the'relativesolubilities of th copper compounds encountered may be considered.

The sulfides of copper are the most insoluble compounds of the metal.The mercaptides by reason of analogous structure exhibit similarsolubilities in water, but are slightly more soluble in oils due to theorganic nature of the alkyl or aryl group present in the mercaptidemolecule.

The sulfides of copper have a solubility of about 0.00033 gram per literof Water and an,infinitesimal solubility in hydrocarbon oils; thesolubility of copper methyl mercaptide is approximately 0.000003 gramper liter of cracked naphtha, or about one-hundredth the solubility ofcopper sulfide in water. These solubility figures are based on extremelysensitive colorimetric tests, especially devised to indicate thepresence and concentration of copper in hydrocarbon oil.

The following table shows the approximate solubilities of copper saltsin oils, or the extent to which oil-soluble copper compounds are formedby contact of the oils with said copper salts for e24 hour period.

Table I Oil-soluble Copper salt Hydrocarbon oil 2 5 2? copper ppcompounds Parts per Grams per 1000 cc.

million ofoil Copper Oxide Doctor-sweet cracked naphtha. Greater than 1.0.0003 (approx.) .do d 0 0003 (approx) Copper carbonate (basic)...Copper hydroxide Copper phosphatem Copper cyanide (KCN Copper silicateCopper sulfite Copper-n-butyl-mercaptrde Copper-t-butyl-mercaptideCopper-ethyl-mercap 0.0003 (approx.) 0.0003 (epprox.) 0.0003 (approx).0003 (approx) .0003 (approx.) 0.0003 (approx) I Sp. gr. of naphthataken as 0.75.

wise possess marked resistance to oxidation processes which would changesaid insoluble copper compounds to more active forms which would beinjurious to the oil.

Oil-soluble copper compounds which may be formed in complex hydrocarbonoil mixtures, particularly in petroleum distillates, are usuallymercaptides or salts of acidic components such as cresylic andnaphthenic acids. Such compounds may be more soluble than copper ethylmercaptide, and likewise may not be removed from an oil in which saidcompounds are dissolved unless the method of treating or stabilizationforms therewith copper compounds less soluble than copper ethylmercaptide. For example, after a cracked naphtha has been in contactwith copper oxide, copper carbonate or copper phosphate, sensitive testsshow the presence of traces of copper remaining in the naphtha, whereasa portion of the same naphtha after prolonged contact with copper methylmercaptide' shows no evidence of dissolved'coppercompounds. Further, thesmall amounts of copper salts resent in a cracked gasoline which hasbeen sweetened with acupric chloride solution. may be removed by addingthereto a controlled amount of methyl mercaptan to convert the moresoluble copper compounds into the less soluble copper methyl mercaptide.Complete removal It will be seen from the values listed in Table I thatcomplete removal of copper from an oil may not be accomplished bycontacting said oil with a reagent to form any of the copper saltslisted. -This fact is based on experimental data which proves that thedeterioration of an oil due to dissolved copper is not prevented unlessthe coppercontent of said oil is reduced to a value less than 0.1 p. p.m. as shown in Table II.

--Thus in order to prevent the deterioration of a hydrocarbon oil whichhas been treated with a copper-containing 1eagent,.it is necessary totreat said oil order to reduce the amount of dissolved copper to a valueless than 0.1 p. p. m. This is accomplished according to our inventionEXAMPLE I A sample of cracked gasoline which had been sweetened bytreatment with a solution containing cupric chloride was separated fromthe copper reagent and divided into two parts. One partwas storedwithout further treatment. To

'reagents were then stored shaken until the oil was saturated with thecopper compound and an excess remained. Portions of this gasoline werethentreated with various reagents to form copper than copper ethylmercaptide. Samples of each portion of gasoline stabilized with thevarious for comparison with a stored sample of the original gasoline andwith the original gasoline saturated with copper ethyl mereaptide. Thetabulation ofresults is given below: a

Table III 01.1? Color Color No. Gasoline sample Copper test inal g 7 g 1color storage storage 1 Cracked gasoline-no additional treatment Negativ+24 +22 +21 2 Cracktgg gasoline-saturated with solid copper-ethyl-mer-Podsiizive, approx. +24 +16 cap a. r p. p. m. 3 #2 sample-added 0.006per cent methyl mercaptan followed Negative, less +24 +22 +21 by waterwash. 7 than 0.1 p.p.m. 4 #2 sample-plus 2 per cent sour vapor recoverygasoline condo +24 +21 taining 0.01 per cent methyl mercaptan. 5 #2sIangliir-intimatelycontactedwith alkaline aqueous solution .do +M +22+21 0 1 zone. 6 #2 sample-contacted with ammoniacal solution 0! alphado+24 +22 +21 benzoinoxime. 7 #2 sample-contacted with aqueous solution ofthionaiide +24 +22 +21 8 #2dsampleuTlcoliiiltacted with aqueous solutionoi 5.7-dibromohy- +24 +22 +21 roxy o e. 9 #2 sample-contacted withammoniacal solution of diethyldi- +24 +22 +21 thiocarbonate.

the other portion was added a solution of methyl mercaptan insulfur-free hexane solution, the quantity added being sufllcient tocause the gasoline to have a methyl mercaptan content of 0.003 weightper cent. After the addition of the mercaptamthe gasoline was allowed tostand for two hours, after which it was washed with water and stored.The results of this stabilizing treat- These examples are illustrativeof the manner in which deterioration is prevented in hydrocarbon oilscontaining soluble copper compounds, according to the practice of thisinvention and the critical value for allowable copper concentration inoil which is stable with regard to color and gum formation in storage isthus disclosed.

ment are shown below: we claim 28: 5 a '0. its so a r ppearan a rGasoline samples Copper test 31 days, days, Storage storage Crackedgasoline, unstabilized Positive, greater than i p. p. m. +24 -16 Darkbrown, gummy. Cracked gasoline plus 0.003 per cent Negative, less than0.1 p. p. m +24 +23 +22 color.

methyl meroaptanJ l This gasoline was doctor sweet; no trace ofmereaptan after two days.

v EXAMPLE II A sample of the same gasoline described in stabilizingreaction was brought about by the addition to one portion of thegasoline of sumcient sour vapor recovery gasoline to amount to 2 percent by volume. This vapor recovery gasoline contained approximately .01weight per cent of methyl mercaptan. The results of this stabilizationare illustrated below:

' Example I was similarly treated except that the i 1. In the process ofsweetening hydrocarbon oil with copper reagents, the step of stabilizingthe sweetened oil to prevent deterioration due to retained oil solublecopper salts which comprisesi adding a small quantity of a. stabilizingagent comprising dithizone.

2. The process as in claim 1 in which the stabilizing agent is analkaline aqueous solution ofdithizone.

- Color Appearance. Gasoline sample Copper test inai I t days daysstorage storage Cracked gasolinecopper treatedunstabilized Positive,greater than 0.1 p. p. 111.. +24 -16 Dark brown. Cracked gasoline-coppertreated plus 2 percent Negative, less than 0.1 p. p. 111.... +24 +23 +220010 (vol.) 0! sour vapor recovery gasoline 1 This gasoline was doctorsweet. I

Examrm 111 To a sample of doctorsweet cracked gasoline WALTER. A.scmizu. GRAHAM H. snoa'r.

salts less soluble I

